The horizon is borrowed from Sachsenring, by Andre Streu et al.
Grandstands are from update packages recently released ... but I can't remember/discover the sources ... if anyone recognizes the grandstands, please let me know who did 'em.

Lord luv all those Geniuses who created the myriad tools used to build GPL tracks.
And mazel tov to Papyrus for creating the best sim ever: Grand Prix Legends

I think so, although maybe the original layout extended further down the Autobahn than the GPL version?

I can add: Montjuic layout is from 1933, and many of the German tracks, like Schleizer Dreieck, are pre-war too, e.g. Schottenring, Sachsenring, Solitude, Nurburgring, and other GP layouts like Spa. But, these would need textures changed, from 60s to pre-50s, to meet your criteria . I guess Indy falls into that category as well.

There are 30s versions of Avus you can dl but they're not the best unfortunately.

The shorter version with its 50s and 60s variants seem really well made though.
50s one has the nicer layout of the two

Make sure you install the gpl 67 long track patch or whatever it was called.
Basically, the one that lets you set harder suspension than the original game. You need it to stop you bottoming on the wall of death. Otherwise you have to slow down earlier, else if you bottom bad then you basically die.